1. Field of the Invention
The present invention relates to an image recording apparatus having an array light source, and particularly to an image recording apparatus which can realize high-quality and high-density image recording at a high speed.
2. Description of the Related Art
In a conventional image recording apparatus, for example, laser light modulated in accordance with an image signal is emitted from a laser light source, scanned in a main scanning direction by a polygon mirror, and a photosensitive drum rotating in a sub-scanning direction is exposed to the laser light scanned by the polygon mirror, so that an electrostatic latent image is formed on the photosensitive drum by this scanning exposure, and image recording is realized on the basis of this electrostatic latent image.
However, according to such a light deflection type image recording apparatus using a polygon mirror, there is a limit in making the recording speed high because there is also a limit in making the rotation velocity of the polygon mirror high.
Therefore, in order to make the recording speed of an image recording apparatus high, there has been considered an image recording apparatus which does not use a polygon mirror but use an array light source which is driven in accordance with the pattern of an image to be recorded and emitting a plurality of light beams.
A conventional image recording apparatus which does not use a polygon mirror is, for example, disclosed in Japanese Patent Unexamined Publication No. Sho-64-42667. This image recording apparatus has a structure in which a surface light-emitting laser array is disposed near a photosensitive drum to perform exposure of the photosensitive drum directly. According to this image recording apparatus, it is considered that high-speed image recording can be performed by driving the surface light-emitting laser array at a high velocity, and driving the photosensitive drum at a rotation velocity corresponding to the driving velocity of the surface light-emitting laser array.
According to the conventional image recording apparatus, however, the surface light-emitting laser array is disposed to directly face the photosensitive drum, and the degree of focusing of laser light of the surface light-emitting laser array is not sufficient. Accordingly, it is impossible to perform high-density image recording with high quality, such as 1,200 dpi required recently. On the other hand, even if a rod lens array is disposed between the surface light-emitting laser array and the photosensitive drum to increase the degree of focusing, the lens diameter of any lens element becomes smaller as the density of picture elements becomes higher. As a result, the recording density can not be increased because of reduction in MTF (Modulation Transfer Function). At the same time, the focal depth becomes so small that it is difficult to accurately attach the array light source having a fear to produce more or less warp, to the photosensitive member, and it is therefore difficult to perform focusing with the surface light-emitting laser array as a whole.